Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 3.2.1.1) constitute a group of enzymes, which catalyzes hydrolysis of starch and other linear and branched 1,4-gluosidic oligo- and polysaccharides.
There is a long history of industrial use of alpha-amylases in several known applications such as detergent, baking, brewing, starch liquefaction and saccharification, e.g., in preparation of high fructose syrups or as part of ethanol production from starch. These and other applications of alpha-amylases are known and utilize alpha-amylases derived from microorganisms, in particular bacterial alpha-amylases.
Among the first bacterial alpha-amylases to be used was an alpha-amylase from B. licheniformis, also known as Termamyl, which has been extensively characterized and the crystal structure has been determined for this enzyme. Alkaline amylases, such as AA560 (SEQ ID NO: 2), disclosed in WO 00/60060, form a particular group of alpha-amylases that have found use in detergents. Many of these known bacterial amylases have been modified in order to improve their functionality in a particular application.
Termamyl and many highly efficient alpha-amylases required calcium for activity. In the crystal structure for Termamyl it was found that four calcium atom were bound in the alpha-amylase structure coordinated by negatively charged amino acid residues. This requirement for calcium is a disadvangtage in applications where strong chelating compounds are present, such as in detergents or during ethanol production from whole grains, where plant material comprising high amount of natural chelaters such as phytate is hydrolysed using alpha-amylases.
Calcium-insensitive amylases are known, e.g., the alpha-amylases disclosed in EP 1022334 and WO 03/083054, and a Bacillus circulans alpha-amylase having the sequence disclosed in UNIPROT:Q03657, but these amylases are inferior to many of the calcium-sensitive amylase when it comes to starch hydrolysis and starch removal in various applications.
It would therefore be beneficial to provide variants of a calcium-sensitive alpha-amylase with reduced calcium sensitivity compared to its parent enzyme.